STORY DRIFT DEFINITION IN ETABS

STORY DRIFT DEFINITION IN ETABS

STORY DRIFT DEFINITION IN ETABS

Hello, I would like to have some information about the exact way ETABS calculates the sory drifts. For example if a point is selected in deformed shape of reponse spectrum load case, ETABS displaces both displacements and drifts. What I can't understand is why the difference between the displacements in two adjacents floors divided by the floor height, is not equal to the value of the story drift calculated by ETABS.

RE: STORY DRIFT DEFINITION IN ETABS

This may be due to the fact that ETABS reports absolute and total horizontal displacements at each floor (and deducts one from the floor above to report inter-storey drift), including the displacemnet caused by rotational deformation (this is only an issue in tall slender structures). In my opinion the lower values (excluding effects of whole-body rotation) are the correct inter-story drifts, as these are relevant to servicibility issues.